地域在住高齢者における三軸加速度センサー内蔵活動量計による身体活動と座位行動の実態および生活機能との関連性

Considerable evidence shows that higher levels of physical activity (PA) in late life are associated with reduced risks of several chronic diseases, better physical and mental health, as well as lower rate of all-cause mortality.In contrast, sedentary behavior (SED), such as sitting or reclining in free-living daily condition, has recently emerged as a new public health risk, independent of PA levels.To date, most of the evidence has primarily relied on subjective measurements of these behaviors, which are prone to a variety of biases, particularly in older adults.Studies with more accurate assessment of the daily levels of PA and SED, such as accelerometer, are needed for better understanding the current population levels of PA and SED, and quantifying the does-response relationships with health outcomes in older adults.Therefore, the doctoral thesis had the following two objectives: (1) to objectively assess daily PA and SED in community-dwelling older adults, using tri-axial accelerometers; (2) to evaluate the associations between these objectively measured PA and SED and selected health conditions such as functional disability and cognitive function in community-dwelling older adults.iii Tri-axial accelerometer-determined daily physical and sedentary behavior of suburban community-dwelling older Japanese adults (Study 1)Participants of this study were from the baseline survey of the Sasaguri Genkimon Study (SGS-1), who were 65 years or older and not certified as those requiring long-term care.Levels of PA and SED were assessed objectively for seven consecutive days using tri-axial accelerometer.A total of 1,739 participants (median age: 72 years, men: 38.0%) with valid accelerometer data were included.Overall, participants in the present study spent 54.5% of their waking time being sedentary, and only 5.4% was moderate-to-vigorous physical activity (MVPA).Women accumulated more minutes of light physical activity (LPA) and MVPA compared with men.In contrast, men spent more time being sedentary.Mean steps per day did not differ between sexes.Furthermore, participants with higher body mass index (BMI ≥25) had lower PA levels, and longer SED compared with those with lower BMI (BMI <25).PA levels were lower and SED was longer with age.The present study is the first to demonstrate that the levels of PA and SED differed by sex, age, and BMI in Japanese community-dwelling older adults.The findings also showed a high level of SED and low level of PA in the Japanese older population.Data presented in the study will enable further investigation of additional determinants of PA and SED in order to develop effective iv population-based intervention strategies to promote PA and reduce prolonged SED in the Japanese population and possibly other rapidly aging societies. Associations of tri-axial accelerometer determined sedentary time and breaks in sedentary time with disability in instrumental activities of daily living in community-dwelling older adults (Study 2)Study 2 was performed to examine cross-sectional associations of objectively measured sedentary time (ST) and breaks in sedentary time (BST) with instrumental activities of daily living (IADL) disability.As in Study 1, participants of this study were from the SGS-1.SED (such as ST and BST) and PA were measured using a tri-axial accelerometer.BST was defined as at least 1 minute where the intensity of activity rose up to or above 1.5 metabolic equivalents (METs) following a sedentary bout.Disability was defined as inability in at least one of IADL tasks using the Tokyo Metropolitan Institute of Gerontology Index of Competence.After adjusting for potential confounders and MVPA, longer ST was significantly associated with higher likelihood of IADL disability, whereas greater number of BST was associated with lower likelihood of IADL disability.ST and BST remained statistically significant after mutual adjustment with odds ratio of 1.30 [95% confidence interval (CI): 1.00-1.70]and 0.80 (95% CI, 0.65-0.99),respectively.After adjusting for confounders and ST, there were no v significant association between MVPA and IADL disability.This study first demonstrated that shorter ST and higher number of BST were associated with lower risk of IADL disability independent of MVPA, and that the association for ST was independent of BST, and vice versa.These findings suggest not only total ST but also the manner in which it is accumulated may contribute to the maintenance of functional independence in older adults. Association between tri-axial accelerometer-determined daily physical activity and cognitive function: a longitudinal population-based cohort study (Study 3)Participants for this study were individuals who had participated in both baseline (SGS-1) and the first follow-up phrase of Sasaguri Genkimon Study (SGS-2).A total of 672 community-dwelling older adults (mean age: 72.3 years, male: 39.9%) without dementia at baseline were involved in this study.Total PA including LPA and MVPA was measured by a tri-axial accelerometer.Cognitive function was assessed by the Japanese version of Montreal Cognitive Assessment (MoCA-J).In the multiple regression model, total physical activity was not associated with the follow-up MoCA-J score (regression coefficient: -0.04; 95% CI: -0.10 to 0.01; p=0.12), after adjusting for socio-demographic and lifestyle factors, as well as physical function, distress, depression, vascular-related diseases and baseline MoCA-J score.There was no linear vi relationship between objective measured total PA and follow-up cognitive function over 2 years in this cohort.Findings in the present study indicated a longer follow-up period might be needed to assess the relationship between physical activity and normal cognitive aging.In conclusion, this doctoral thesis reveals that Japanese older adults spent majority of the day being sedentary and accumulated few minutes of MVPA, and confirms that SED is a distinct concept from insufficient MVPA and has independent effects on health outcomes in older adults.These findings highlights the need of reducing overall time spent in SED in community-dwelling older adults to optimize their health, beyond encouraging PA.In addition, it also suggests breaking up prolonged sedentary time may be beneficial for the maintenance of functional capacity in older adults.Although no significant association between accelerometer-determined PA and cognitive function was observed, the doctoral thesis has shown the feasibility and utility of the accelerometer in longitudinal, large-scale epidemiology studies.Further studies will be performed investigate the associations of these objectively measured behaviors with other health conditions and the incidence of hard clinical endpoints (e.g., dementia, all-cause mortality) to facilitate development of guidelines related to PA and SED in this population.vii

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